This disclosure is directed to systems and methods for improving image quality, particularly with regard to formed images including reverse fine features.
In the process of image formation, there are unique difficulties associated with rendering and/or forming reverse features on an image output medium. Reverse features are those in which white, near-white or essentially transparent images are to be disposed on the output image receiving medium within an area including a dark or color background.
Conventional methods for enhancing image quality in produced images are directed principally at attempting to ensure that edges of such images are crisply defined. Conventional methods for attempting to ensure such crispness and/or sharpness, particularly with regard to text and line objects, tend to lead to a blending of individual opposing edges that wash out a small text font or fine line object image particularly as the size of the image is reduced.
Depending on the image formation method employed by an image forming device, and on a dot-per-inch (DPI) resolution for the formed image, an ability to render and/or print finely-defined features, particularly in reverse printing may be varyingly affected. A particular image forming methodology by which such images maybe rendered less perceptible as the width of fine lines or the size of fonts are reduced involves electrostatic and/or xerographic image formation.
In many xerographic image forming systems and/or devices, for example, fill-in artifacts that are included to enhance crispness remain perceptible when printing reverse fine features, such as fine lines or small text fonts, in white on a dark or color background. As such, these fill-in artifacts may obliterate the fine lines and/or small text fonts. These problems associated with printing reverse fine features are increasingly pronounced in circumstances when, for example, high addressability halftones are employed at the edges of adjacent background pixels, and/or when the background color contains an excessive toner amount. Bleed of the fine edge adjustments into the white fine line or small text font areas result in the reverse fine features becoming indistinct or difficult to recognize and/or read.
Such difficulties arise, as introduced briefly above, because, for text and line objects, sharpness is generally an important attribute in evaluating image quality. Image forming systems enable enhanced sharpness by various methods including modifying edge pixels of an object to employ high addressability halftone screens (or outlining cells, e.g., 600 lpi line screens), while still employing base dot screens for the non-edge pixels (e.g., 200 dpi dot screens). This method can be particularly effective in enhancing sharpness of the formed image in reverse printing lines and text characters when the involved object is white, and of normal to large size, and the background is colored. High addressability halftones are applied to the colored edge pixels that belong to the background to enhance this sharpness.
However, for small text fonts and fine lines, simple readability becomes a more important attribute than individual object or character sharpness. Technologies and image forming methods designed to enable edge pixels of an object to use high addressability screens tend to exacerbate the readability problem of fine lines and small text fonts in many cases. Among other reasons, this may be because high addressability halftone dots, which are separated by small white openings of an object, such as a fine line or small text font character, are too close to each other. The interaction of the high addressability halftone dots non-linearly amplifies image development. Halftone dots tend to fill in the intended white opening and distort the appearance of the fine line or small text font character to a point that the white object becomes unreadable in part or in its entirety.
Among conventional solutions that are intended to address this problem are methods that disable the outlining cells for reverse objects when the objects are below a certain size threshold. This approach leaves the white areas more perceptible, but the objects may become too blurry when the background is lighter. Further, this approach still suffers from the fill-in artifact when the background coloring is rendered with a greater toner pile. Additionally, this approach tends to introduce a size discontinuity when objects with sizes just above and just below the threshold value for enabling and disabling cells for reverse objects are placed next to each other.
Another method by which to attempt to solve the non-readability problem for fine lines involves globally thickening a stroke size for the thin reverse lines. This method, however, also thickens the positive or color line. Although it can be implemented as size/color dependent, this method often must be applied to the page description language (PDL) or object level, for example, before flattening and rasterizing. This method is, therefore, not very straightforward.
Increasing the size of reverse printed small text font characters at the object level may make the fonts bigger instead of just thicker. Methods for accomplishing this are also not precisely straightforward. They are often system level settings and may require restart and/or additional user interaction to implement. Ultimately too, because these methods are not straightforward, they may result in undesirable image formation within the image forming device.